Pigmented phase change inks with dispersant and synergist

ABSTRACT

A phase change ink composition includes an ink vehicle and at least one pigment, wherein the ink composition is substantially solid at room temperature and includes at least one dispersant for the at least pigment and at least one synergist.

BACKGROUND

Described herein are phase change ink compositions comprising an inkvehicle and at least one pigment, wherein the ink composition issubstantially solid at room temperature and includes at least onedispersant and at least one synergist. The dispersant and synergistallow the pigment to be well dispersed in the solid phase change inkcomposition without adversely affecting the hardness of the ink. Thephase change inks are suitable for ink jet printing processes

Advantages achieved by the phase change inks herein include that the useof at least one dispersant and at least one synergist results in verystable inks, as determined by the measurement of particle size aftersubjecting the inks to high temperatures, for example 100° C., forextended periods of time, for example 1 week. Furthermore, the amount ofdispersant, in particular dispersants that are liquid or paste-like atroom temperature, required to stabilize the pigment in the ink can bereduced without sacrificing ink stability, thereby also achieving areduction in the tackiness of the ink during processing and on imageprints from the subsequent printed ink.

REFERENCES

Ink jet printing processes may employ inks that are solid at roomtemperature, for example from about 20° C. to about 27° C., and that areliquid at elevated jetting temperatures, for example of from about 60°C. to about 150° C. Such inks are typically referred to as hot melt inksor phase change inks.

In ink jet printing processes employing a phase change ink, thesubstantially solid ink is melted by the heater in the printingapparatus and jetted as a liquid in a manner similar to that ofconventional liquid ink jet printing. Upon contact with the printingsubstrate, which can be either an intermediate transfer medium, such asan aluminum drum, or the receiving substrate, such as paper ortransparency material, the molten ink solidifies rapidly, desirablysolidifying at a rate enabling the colorant to substantially remain onthe surface of the substrate instead of being carried into the substrate(for example, paper) by capillary action, thereby enabling higher printdensity than is generally obtained with liquid inks. Advantages of aphase change ink in ink jet printing thus include little or noevaporation of the ink's components, elimination of potential spillageof the ink during handling, a wide range of print density and quality,minimal paper cockle or distortion, and enablement of indefinite periodsof nonprinting without the danger of nozzle clogging, even withoutcapping the nozzles.

U.S. Patent Application Publication No. 2008/0098929, incorporatedherein by reference in its entirety, describes a phase change ink havingan ink vehicle, at least one colorant, at least one triamide and atleast one bis-urethane. The at least one triamide and at least onebis-urethane can assist in dispersing colorants, such as pigments likecarbon black, in non-polar ink vehicles.

U.S. Patent Application Publication No. 2008/0098927, incorporatedherein by reference in its entirety, describes a pigmented phase changeink composition comprising an ink carrier, a dispersing agent, andpigment particles. The ink can be resistant to substantial aggregationand settling of the pigment particles in the melt and even when exposedto freeze thaw cycles.

U.S. Pat. No. 7,407,539, incorporated herein by reference in itsentirety, describes a phase change ink comprising (a) a colorant and (b)a phase change ink carrier, said carrier comprising (i) a branchedtriamide and (ii) a polyethylene wax having an average peak molecularweight of from about 350 to about 730, a polydispersity of from about1.03 to about 3.0, and an asymmetrical molecular weight distributionskewed toward the high molecular weight end.

U.S. Pat. No. 7,293,868, incorporated herein by reference in itsentirety, describes ink compositions that include one or more radiationcurable oil soluble components and one or more thermal solvents, as wellas methods of preparing such ink compositions and methods of using suchink compositions.

U.S. Pat. No. 6,860,930, incorporated herein by reference in itsentirety, describes a phase change ink composition comprising (a) acolorant and (b) a carrier comprising a polyamide, wherein the polyamidecomponent of the carrier contains at least about 10 percent by weight ofa branched triamide.

Solid inks typically employ dyes as colorants. Certain dyes are veryexpensive, contributing a significant amount to the ink cost, and maysuffer from poor lightfastness, dye migration/bleeding issues and/orpoor solubility. Pigments can be significantly less costly than dyes andoffer excellent color and thermal stability, and improved colorantmigration resistance properties.

In phase change inks, a dispersant may be used to assist in stabilizingthe dispersion of the pigment of the ink in the ink vehicles. In orderto effectively stabilize the pigment, higher dispersant loadings havebeen used, for example loading amounts of about 5% by weight or more ofthe ink. However, the higher loading of the dispersant may adverselyaffect the hardness of the ink, resulting in an ink with relatively softand tacky characteristics. Prints formed with such an ink may experiencehigher incidences of sticking and transfer to a transfuse drum usedduring the image formation process. While decreasing the amount ofdispersant can avoid undesirable softening of the ink, the pigment maynot be sufficiently stabilized in the ink, creating other potentialproblems such as long term ink stability, which can negatively impactjetting reliability.

What is desired is a phase change ink composition that includes astabilized pigmented ink system that is not soft and tacky.

SUMMARY

These and other objects are achieved herein, where, in embodiments,disclosed is a phase change ink composition comprising an ink vehicleand at least one pigment, wherein the ink composition is substantiallysolid at room temperature and includes at least one dispersant and atleast one synergist for the at least one pigment, and wherein theaverage particle size of the ink composition, when stored at 120° C. for30 days, increases by less than 20% from an average particle size of theink composition when freshly made.

In further embodiments, described is a phase change ink compositioncomprising an ink vehicle and at least one pigment, wherein the inkcomposition includes at least one dispersant for the at least onepigment in an amount of from about 0.1% by weight to about 1.5% byweight of the ink composition, and at least one synergist in an amountof from about 0. 1% by weight to about 5% by weight of the pigment inthe ink composition.

In still further embodiments, described is a phase change inkcomposition comprising an ink vehicle and at least one pigment, the inkvehicle comprising at least one wax and at least one amide resin,wherein the ink composition includes at least one dispersant for the atleast one pigment and at least one synergist, the at least one synergistincluding a functional group that adsorbs to the surface of the at leastone pigment and being insoluble in the wax, the at least one dispersantcomprising a portion interactive with the at least one synergist and aportion soluble in the wax.

Embodiments

The phase change inks herein are substantially solid at temperatures ofabout 20° C. to about 27° C., for example room temperature, andspecifically are substantially solid at temperatures below about 40° C.However, the inks chance phase upon heating, and are in a molten stateat jetting temperatures. Thus, the inks have a viscosity of from about 1to about 40 centipoise (cP), such as from about 5 to about 15 cP or fromabout 8 to about 12 cP, at an elevated temperature suitable for ink jetprinting, such as temperatures of from about 50° C. to about 150° C.

In this regard, the inks herein may be regarded as low energy inks. Lowenergy inks are solid at a temperature below about 40° C. and have aviscosity of from about 5 to about 15 cP at a jetting temperature offrom about 50° C. to about 150° C., such as from about 70° C. to about130° C. or from about 60° C. to about 130° C. The inks jet at lowertemperatures, and thus require lower amounts of energy for jetting.

Any suitable ink vehicle can be employed. Typically, phase change inksinclude at least a wax based vehicle.

The wax in the vehicle may act as a phase change agent in the ink.Specifically, the ink undergoes a phase change by being solid at roomtemperature and molten at jetting temperatures. The wax thus promotesthe increase in viscosity and hardness of the ink as it cools from thejetting temperature, for example from about 75° C. to about 150° C., tothe substrate temperature, which is for example from about 20° C. toabout 65° C.

As used herein, the term wax includes, for example, natural, modifiednatural, synthetic waxes and compounded waxes. Natural waxes may be ofvegetable, animal, or mineral origin. Modified waxes are natural waxesthat have been treated chemically to change their nature and properties.Synthetic waxes are made by the reaction or polymerization of chemicals.Compounded waxes are mixtures of various waxes or of waxes with resinsor other compounds added thereto.

Suitable waxes can include paraffins, olefins such as polymethylene,polyethylene and polypropylene, microcrystalline waxes, ester waxes,fatty acids and other waxy materials, fatty amide containing materials,sulfonamide materials, resinous materials made from different naturalsources (tall oil rosins and rosin esters, for example), and manysynthetic resins, oligomers, polymers, and copolymers and mixturesthereof

Suitable phase change waxes include polyethylene waxes, includinghydroxyl-terminated polyethylene waxes such as mixtures of carbon chainswith the structure CH₃—(CH₂)_(n)CH₂OH, where there is a mixture of chainlengths, n, where the average chain length is in the range of about 16to about 50, and linear low molecular weight polyethylene, of similaraverage chain length. Suitable examples of such waxes include, forexample, UNILIN 350, UNILIN 425, UNILIN 550 and UNILIN 700. All of thesewaxes are commercially available from Baker-Petrolite.

Examples of suitable specific ink vehicles include, for example,ethylene/propylene copolymers, such as those available from BakerPetrolite having the general formula

wherein x is an integer of from about 1 to about 200, such as from about5 to about 150 or from about 12 to about 105. These materials may have amelting point of from about 60° C. to about 150° C., such as from about70° C. to about 140° C. or from about 80° C. to about 130° C. and anumber average molecular weight (Mn) of from about 100 to about 5,000,such as from about 200 to about 4,000 or from about 400 to about 3,000.Commercial examples of such copolymers include, for example, thePOLYWAX® line of waxes from Baker-Petrolite.

The ability of the wax to crystallize contributes to its overallhardness, which imparts strength to the ink. The degree ofcrystallization can be controlled by regulating the degree of branching(that is, irregularity) of the wax. A high degree of linearity of apolyethylene chain generally yields a highly crystalline and hardmaterial. The hardness of the ink is also directly dependent on themolecular weight of the waxy components, such that higher molecularweight waxes afford inks that are relatively harder and potentially morerobust.

Other suitable phase change waxes include alcohol waxes, for example,hydrogenated castor oil, 1-octadecanol, 1,10-decanediol and1,12-dodecanediol. Other examples of mono functional alcohols that canbe employed as phase change waxes herein include 1-tetradecanol,1-pentadecanol, 1-hexadecanol, 1-heptadecanol, 1-nonadecanol,1-eicosanol, 1-tricosanol, 1-tetracosanol, 1-pentacosanol,1-hexacosanol, 1-heptacosanol, 1-octacosanol, 1-nonacosanol,1-tricontanol, 1-dotriacontanol, 1-tritriacontanol, 1-tetratriacontanol.Also suitable are Guerbet alcohols such as 2-tetradecyl 1-octadecanol,2-hexadecyl 1-eicosanol, 2-octadecyl 1-docosanol, 2-nonadecyl1-tricosanol, 2-eicosyl tetracosanol, and mixtures thereof. Suitablediols include 1,8-octanediol, 1,9-nonanediol, 1,13-tridecanediol,1,14-tetradecanediol, 1,15-pentadecanediol, 1,16-hexandecanediol,1,17-heptadecanediol, 1,18-octadecanediol, 1,19-nonadecanediol,1,20-eicosanediol, 1,22-docosanediol, 1,25-pentacosanediol, and mixturesthereof.

Other suitable phase change waxes include carboxylic acid waxes, forexample, UNICID® 350, UNICID® 425, UNICID® 550 and UNICID® 700. All ofthese waxes are commercially available from Baker-Petrolite.

Examples of urethane waxes that may be used include the reaction productof an isocyanate and an alcohol. Examples of suitable isocyanatesinclude monoisocyanates, diisocyanates, triisocyanates, copolymers of adiisocyanate, copolymers of a triisocyanate, polyisocyanates (havingmore than three isocyanate functional groups), and the like, as well asmixtures thereof. Examples of monoisocyanates includen-octadecylisocyanate, hexadecylisocyanate; octylisocyanate; n- andt-butylisocyanate; cyclohexyl isocyanate; adamantyl isocyanate;ethylisocyanatoacetate; ethoxycarbonylisocyanate; phenylisocyanate;alphamethylbenzyl isocyanate; 2-phenylcyclopropyl isocyanate;benzylisocyanate; 2-ethylphenylisocyanate; benzoylisocyanate; meta andpara-tolylisocyanate; 2-, 3-, or 4-nitrophenylisocyanates;2-ethoxyphenyl isocyanate; 3-methoxyphenyl isocyanate;4-methoxyphenylisocyanate; ethyl 4-isocyanatobenzoate;2,6-dimethylphenylisocyante; 1-naphthylisocyanate;(naphthyl)ethylisocyantes; and the like, as well as mixtures thereof.Examples of diisocyanates include isophorone diisocyanate (IPDI),toluene diisocyanate (TDI); diphenylmethane-4,4′-diisocyanate (MDI);hydrogenated diphenylmethane-4,4′-diisocyanate; tetra-methyl xylenediisocyanate (TMXDI); hexamethylene-1,6-diisocyanate (HDI),naphthalene-1,5-diisocyanate; 3,3 ′-dimethoxy-4,4′-biphenyldiisocyanate;3,3′-dimethyl-4,4′-bimethyl-4,4′-biphenyldiisocyanate; phenylenediisocyanate; 4,4′-biphenyldiisocyanate;trimethyl-1,6-diisocyanatohexane, tetramethylene xylene diisocyanate;4,4′-methylenebis(2,6-diethylphenyl isocyanate);1,12-diisocyanatododecane; 1,5-diisocyanato-2-methylpentane;1,4-diisocyanatobutane; dimer diisocyanate and cyclohexylenediisocyanate and its isomers; uretidione dimers of HDI; and the like, aswell as mixtures thereof Examples of triisocyanates or their equivalentsinclude the trimethylolpropane trimer of TDI, and the like, isocyanuratetrimers of TDI, HDI, IPDI, and the like, and biuret trimers of TDI, HDI,IPDI, and the like, as well as mixtures thereof. Examples of higherisocyanate functionalities include copolymers of TDI/HDI, and the like,and MDI oligomers, as well as mixtures thereof.

In embodiments, the wax is functionalized with one or more curablemoieties, including, for example, vinyl ethers; epoxides, such ascycloaliphatic epoxides, aliphatic epoxides, and glycidyl epoxides;oxetanes; (meth)acrylates, that is, acrylates and methacrylates; and thelike.

Additional examples of wax materials that may be used as the ink vehicleare set forth in, for example, U.S. Pat. No. 6,860,930, incorporatedherein by reference in its entirety.

The ink vehicle may also include fatty amides, such as monoamides,tetra-amides, mixtures thereof, and the like, for example such asdescribed in U.S. Pat. No. 6,858,070, incorporated herein by referencein its entirety. Suitable monoamides may have a melting point of atleast about 50° C., for example from about 50° C. to about 150° C.,although the melting point can be above or below these temperatures.Specific examples of suitable monoamides include, for example, primarymonoamides and secondary monoamides. Stearamide, such as KEMAMIDE Savailable from Witco Chemical Company and CRODAMIDE S available fromCroda, behenamide/arachidamide, such as KEMAMIDE B available from Witcoand CRODAMIDE BR available from Croda, oleamide, such as KEMAMIDE Uavailable from Witco and CRODAMIDE OR available from Croda, technicalgrade oleamide, such as KEMAMIDE O available from Witco, CRODAMIDE Oavailable from Croda, and UNISLIP 1753 available from Uniqema, anderucamide such as KEMAMIDE E available from Witco and CRODAMIDE ERavailable from Croda, are some examples of suitable primary amides.Behenyl behenamide, such as KEMAMIDE EX666 available from Witco, stearylstearamide, such as KEMAMIDE S-180 and KEMAMIDE EX-672 available fromWitco, stearyl erucamide, such as KEMAMIDE E-180 available from Witcoand CRODAMIDE 212 available from Croda, erucyl erucamide, such asKEMAMIDE E-221 available from Witco, oleyl palmitamide, such as KEMAMIDEP-181 available from Witco and CRODAMIDE 203 available from Croda, anderucyl stearamide, such as KEMAMIDE S-221 available from Witco, are someexamples of suitable secondary amides. Additional suitable amidematerials include KEMAMIDE W40 (N,N′-ethylenebisstearamide), KEMAMIDEP181 (oleyl palmitamide), KEMAMIDE W45 (N,N′-thylenebisstearamide), andKEMAMIDE W20 (N,N′-ethylenebisoleamide).

Additional examples of suitable ink vehicle components for the phasechange inks include rosin esters, such as glyceryl abietate (KE-100®);polyamides; dimer acid amides; fatty acid amides, including ARAMID C;epoxy resins, such as EPOTUF 37001, available from Riechold ChemicalCompany; fluid paraffin waxes; fluid microcrystalline waxes;Fischer-Tropsch waxes; polyvinyl alcohol resins; polyols; celluloseesters; cellulose ethers; polyvinyl pyridine resins; fatty acids; fattyacid esters; poly sulfonamides, including KETJENFLEX MH and KETJENFLEXMS80; benzoate esters, such as BENZOFLEX S552, available from VelsicolChemical Company; phthalate plasticizers; citrate plasticizers; maleateplasticizers; polyvinyl pyrrolidinone copolymers; polyvinylpyrrolidone/polyvinyl acetate copolymers; novolac resins, such as DUREZ12 686, available from Occidental Chemical Company; and natural productwaxes, such as beeswax, montan wax, candelilla wax, GILSONITE (AmericanGilsonite Company), and the like; mixtures of linear primary alcoholswith linear long chain amides or fatty acid amides, such as those withfrom about 6 to about 24 carbon atoms, including PARICIN 9 (propyleneglycol monohydroxystearate), PARICIN 13 (glycerol monohydroxystearate),PARICIN 15 (ethylene glycol monohydroxystearate), PARICIN 220(N(2-hydroxyethyl)-12-hydroxystearamide), PARCIN 285(N,N′-ethylene-bis-12-hydroxystearamide), FLEXRICIN 185(N,N′-ethylene-bis-ricinoleamide), and the like. Further, linear longchain sulfones with from about 4 to about 16 carbon atoms, such asdiphenyl sulfone, n-arnyl sulfone, n-propyl sulfone, n-pentyl sulfone,n-hexyl sulfone, n-heptyl sulfone, n-octyl sulfone, n-nonyl sulfone,n-decyl sulfone, n-undecyl sulfone, n-dodecyl sulfone, n-tridecylsulfone, n-tetradecyl sulfone, n-pentadecyl sulfone, n-hexadecylsulfone, chlorophenyl methyl sulfone, and the like, are suitable inkvehicle materials.

The ink vehicle may comprise from about 25% to about 99.5% by weight ofthe ink, for example from about 30% to about 90% or from about 50% toabout 75% by weight of the ink.

The ink may also include therein at least one amide resin. The amideresin may act as a dispersant for the pigment(s) of the ink. The amideresin may be a triamide or higher order amide (such as tetraamide andthe like) resin.

Suitable triamides for use herein include linear triamides, which aremolecules in which all three amide groups are contained within a singlehydrocarbon backbone. Examples of linear triamides include thosetriamides having the following formulas:

R can be any hydrocarbon having from about 1 to about 200, carbon atoms,such as from about 25 to 150 carbon atoms or from about 30 to about 100carbon atoms.

Linear triamides can farther include those wherein the three amidegroups are contained within a single hydrocarbon backbone, even thoughthe normal depiction of the molecule would suggest the amide groups areon different branches. One example of such a triamide can be expressedby the following formula:

which can also be depicted as:

In embodiments, the triamide may also be a branched triamide. Examplesof suitable branched triamides include those triamides disclosed in U.S.Pat. No. 6,860,930, which is incorporated herein in its entirety byreference. Any branched triamide disclosed in U.S. Pat. No. 6,860,930,is suitable for use herein. Examples of branched triamides suitable foruse herein include those having the formulas:

and the like are disclosed in U.S. Pat. No. 6,860,930. In such branchedtriamides, R₁ and R₂ may be (i) an alkylene group (including linear,branched, saturated, unsaturated, cyclic, substituted, and unsubstitutedalkylene groups, and wherein hetero atoms, such as oxygen, nitrogen,sulfur, silicon, phosphorus, and the like either may or may not bepresent in the alkylene group), having from about 3 carbon atoms toabout 200 carbon atoms, such as from about 15 carbon atoms to about 150carbon atoms or from about 21 carbon atoms to about 100 carbon atoms,although the number of carbon atoms can be outside of these ranges, (ii)an arylene group (including unsubstituted and substituted arylenegroups, and wherein hetero atoms, such as oxygen, nitrogen, sulfur,silicon, phosphorus, and the like either may or may not be present inthe arylene group), having from about 6 carbon atoms to about 200 carbonatoms, such as from about 10 carbon atoms to about 150 carbon atoms orfrom about 14 carbon atoms to about 100 carbon atoms, although thenumber of carbon atoms can be outside of these ranges, (iii) anarylalkylene group (including unsubstituted and substituted arylalkylenegroups, wherein the alkyl portion of the arylalkylene group can belinear, branched, saturated, unsaturated, and/or cyclic, and whereinhetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, andthe like either may or may not be present in either or both of the alkylportion and the aryl portion of the arylalkylene group), having fromabout 7 carbon atoms to about 200 carbon atoms, such as from about 8carbon atoms to about 150 carbon atoms or from about 9 carbon atoms toabout 100 carbon atoms, although the number of carbon atoms can beoutside of these ranges, such as benzylene or the like, or (iv) analkylarylene group (including unsubstituted and substituted alkylarylenegroups, wherein the alkyl portion of the alkylarylene group can belinear, branched, saturated, unsaturated, and/or cyclic, and whereinhetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, andthe like either may or may not be present in either or both of the alkylportion and the aryl portion of the alkylarylene group), having fromabout 7 carbon atoms to about 200 carbon atoms, such as from about 8carbon atoms to about 150 carbon atoms or from about 9 carbon atoms toabout 100 carbon atoms, although the number of carbon atoms can beoutside of these ranges, such as tolylene or the like. R_(a), R_(b),R_(c), R_(d), R_(g), R_(h), R_(j), R_(k), R_(p) and R_(q) may eachindependently be (i) a hydrogen atom, (ii) an alkyl group (includinglinear, branched, saturated, unsaturated, cyclic, substituted, andunsubstituted alkyl groups, and wherein hetero atoms, such as oxygen,nitrogen, sulfur, silicon, phosphorus, and the like either may or maynot be present in the alkyl group), in embodiments from about 1 carbonatoms to about 200 carbon atoms, such as from about 6 carbon atoms toabout 150 carbon atoms or from about 10 carbon atoms to about 100 carbonatoms, although the number of carbon atoms can be outside of theseranges, (iii) an aryl group (including unsubstituted and substitutedaryl groups, and wherein hetero atoms, such as oxygen, nitrogen, sulfur,silicon, phosphorus, and the like either may or may not be present inthe aryl group), having from about 6 carbon atoms to about 200 carbonatoms, such as from about 10 carbon atoms to about 150 carbon atoms orfrom about 14 carbon atoms to about 100 carbon atoms, although thenumber of carbon atoms can be outside of these ranges, (iv) an arylalkylgroup (including unsubstituted and substituted arylalkyl groups, whereinthe alkyl portion of the arylalkyl group can be linear, branched,saturated, unsaturated, and/or cyclic, and wherein hetero atoms, such asoxygen, nitrogen, sulfur, silicon, phosphorus, and the like either mayor may not be present in either or both of the alkyl portion and thearyl portion of the arylalkyl group), having from about 6 carbon atomsto about 200 carbon atoms, such as from about 7 carbon atoms to about150 carbon atoms or from about 8 carbon atoms to about 100 carbon atoms,although the number of carbon atoms can be outside of these ranges, suchas benzyl or the like, or (v) an alkylaryl group (includingunsubstituted and substituted alkylaryl groups, wherein the alkylportion of the alkylaryl group can be linear, branched, saturated,unsaturated, and/or cyclic, and wherein hetero atoms, such as oxygen,nitrogen, sulfur, silicon, phosphorus, and the like either may or maynot be present in either or both of the alkyl portion and the arylportion of the alkylaryl group), having from about 6 carbon atoms toabout 200 carbon atoms, such as from about 7 carbon atoms to about 150carbon atoms or from about 8 carbon atoms to about 100 carbon atoms,although the number of carbon atoms can be outside of these ranges, suchas tolyl or the like. R_(d), R_(e) and R_(f) may each independently be(i) an alkyl group as described above, (ii) an aryl group as describedabove, (iii) an arylalkyl group as described above, or (iv) an alkylarylgroup as described above.

The triamide is present in the ink in amounts of from about 0.5 weightpercent to about 40 weight percent, such as from about 5 weight percentto about 18 weight percent or from about 8 weight percent to about 13weight percent of the ink. In embodiments, the amide resin used may bepresent in amounts outside of these ranges, and may also include higherorder amides, such as tetraamides, pentaamides and the like.

One or more urethane resins may be included in the ink composition.Suitable urethane resins are described in, for example, U.S. Pat. No.6,309,453, incorporated herein by reference in its entirety.

The urethane may be present in the ink in amounts of from about 0.5weight percent to about 40 weight percent, such as from about 1 weightpercent to about 8 weight percent or from about 1.5 weight percent toabout 5 weight percent of the ink.

The ink of embodiments may further include conventional additives totake advantage of the known functionality associated with suchconventional additives. Examples of additives are briefly discussedbelow.

Plasticizers may be included in the ink, and may include, for example,pentaerythritol tetrabenzoate, commercially available as BENZOFLEX S552(Velsicol Chemical Corporation), trimethyl titrate, commerciallyavailable as CITROFLEX 1 (Monflex Chemical Company), N,N-dimethyloleamide, commercially available as HALCOMID M-18-OL (C. P. HallCompany), a benyl phthalate, commercially available as SANTICIZER 278(Ferro Corporation), and the like, may be added to the ink vehicle, andmay constitute from about 1 to 100 percent of the ink vehicle componentof the ink. Plasticizers can either function as the ink vehicle or canact as an agent to provide compatibility between the ink propellant,which generally is polar, and the ink vehicle, which generally isnon-polar.

The ink may further include an optional viscosity modifier, such as (1)2-hydroxybenzyl alcohol, (2) 4-hydroxybenzyl alcohol, (3) 4-nitrobenzylalcohol, (4) 4-hydroxy-3-methoxy benzyl alcohol, (5)3-methoxy-4-nitrobenzyl alcohol, (6) 2-amino-5-chlorobenzyl alcohol, (7)2-amino-5-methylbenzyl alcohol, (8) 3-amino-2-methylbenzyl alcohol, (9)3-amino-4-methyl benzyl alcohol, (10) 2(2-(aminomethyl)phenylthio)benzylalcohol, (11) 2,4,6-trimethylbenzyl alcohol, (12)2-amino-2-methyl-1,3-propanediol, (13) 2-amino-1-phenyl-1,3-propanediol,(14) 2,2-dimethyl-1-phenyl-1,3-propanediol, (15)2-bromo-2-nitro-1,3-propanediol, (16) 3-tert-butylamino-1,2-propanediol,(17) 1,1-diphenyl-1,2-propanediol, (18) 1,4-dibromo-2,3-butanediol, (19)2,3-dibromo-1,4-butanediol, (20) 2,3-dibromo-2-butene-1,4-diol, (21)1,1,2-triphenyl-1,2-ethanediol, (22) 2-naphthalenemethanol, (23)2-methoxy-1-naphthalenemethanol, (24) decafluoro benzhydrol, (25)2-methylbenzhydrol, (26) 1-benezeethanol, (27) 4,4′-isopropylidenebis(2-(2,6-dibromo phenoxy)ethanol), (28)2,2′-(1,4-phenylenedioxy)diethanol, (29) 2,2-his(hydroxymethyl)-2,2′,2″-nitrilotriethanol, (30) di(trimethylolpropane),(31) 2-amino-3-phenyl-1-propanol, (32) tricyclohexylmethanol, (33)tris(hydroxymethyl)aminomethane succinate, (34) 4,4′-trimethylenebis(1-piperidine ethanol), (35) N-methyl glucamine, (36) xylitol, ormixtures thereof. When present, the viscosity modifier is present in theink in any effective amount, such as from about 30 percent to about 55percent by weight of the ink or from about 35 percent to about 50percent by weight of the ink.

The ink may optionally contain antioxidants to protect the images fromoxidation and also may protect the ink components from oxidation whileexisting as a heated melt in the printer. Examples of suitableantioxidants include (1) N,N′-hexamethylenebis(3,5-di-tert-butyl-4-hydroxy hydrocinnamamide) (IRGANOX 1098,available from Ciba-Geigy Corporation), (2)2,2-bis(4-(2-(3,5-di-tert-butyl-4-hydroxyhydrocinnamoyloxy))ethoxyphenyl)propane(TOPANOL-205, available from ICI America Corporation), (3)tris(4-tert-butyl-3-hydroxy-2,6-dimethyl benzyl)isocyanurate (CYANOX1790, 41, 322-4, LTDP, Aldrich D12,840-6), (4) 2,2′-ethylidenebis(4,6-di-tert-butylphenyl) fluoro phosphonite (ETHANOX-398, availablefrom Ethyl Corporation), (5)tetrakis(2,4-di-tert-butylphenyl)-4,4′-biphenyl diphosphonite (ALDRICH46,852-5; hardness value 90), (6) pentaerythritol tetrastearate (TCIAmerica #PO739), (7) tributylammonium hypophosphite (Aldrich 42,009-3),(8) 2,6-di-tert-butyl-4-methoxyphenol (Aldrich 25,106-2), (9)2,4-di-tert-butyl-6-(4-methoxybenzyl)phenol (Aldrich 23,008-1), (10)4-bromo-2,6-dimethylphenol (Aldrich 34,951-8), (11)4-bromo-3,5-didimethylphenol (Aldrich B6,420-2), (12)4-bromo-2-nitrophenol (Aldrich 30,987-7), (13) 4-(diethylaminomethyl)-2,5-dimethylphenol (Aldrich 14,668-4), (14)3-dimethylaminophenol (Aldrich D14,400-2), (15)2-amino-4-tert-amylphenol (Aldrich 41,258-9), (16)2,6-bis(hydroxymethyl)-p-cresol (Aldrich 22,752-8), (17)2,2′-methylenediphenol (Aldrich B4,680-8), (18)5-(diethylamino)-2-nitrosophenol (Aldrich 26,951-4), (19)2,6-dichloro-4-fluorophenol (Aldrich 28,435-1), (20) 2,6-dibromo fluorophenol (Aldrich 26,003-7), (21) α-trifluoro-o-creso-1 (Aldrich21,979-7), (22) 2-bromo-4-fluorophenol (Aldrich 30,246-5), (23)4-fluorophenol (Aldrich F1, 320-7), (24)4-chlorophenyl-2-chloro-1,1,2-tri-fluoroethyl sulfone (Aldrich13,823-1), (25) 3,4-difluoro phenylacetic acid (Aldrich 29,043-2), (26)3-fluorophenylacetic acid (Aldrich 24,804-5), (27) 3,5-difluorophenylacetic acid (Aldrich 29,044-0), (28) 2-fluorophenylacetic acid(Aldrich 20,894-9), (29) 2,5-bis (trifluoromethyl)benzoic acid (Aldrich32,527-9), (30) ethyl-2-(4-(4-(trifluoromethyl) phenoxy) phenoxy)propionate (Aldrich 25,074-0), (31) tetrakis (2,4-di-tert-butylphenyl)-4,4′-biphenyl diphosphonite (Aldrich 46,852-5), (32) 4-tert-amylphenol (Aldrich 15,384-2), (33) 3-(2H-benzotriazol-2-yl)-4-hydroxyphenethylalcohol (Aldrich 43,071-4), NAUGARD 76, NAUGARD 445, NAUGARD512, and NAUGARD 524 (manufactured by Uniroyal Chemical Company), andthe like, as well as mixtures thereof The antioxidant, when present, maybe present in the ink in any desired or effective amount, such as fromabout 0.25 percent to about 10 percent by weight of the ink or fromabout 1 percent to about 5 percent by weight of the ink.

The ink can also optionally contain a UV absorber. The optional UVabsorbers primarily protect the generated images from UV degradation.Specific examples of suitable UV absorbers include (1)2-bromo-2′,4-dimethoxyacetophenone (Aldrich 19,948-6), (2)2-bromo-2,5′-dimethoxyacetophenone (Aldrich 10,458-2), (3)2-bromo-3′-nitroacetophenone (Aldrich 34,421-4), (4)2-bromo-4′-nitroacetophenone (Aldrich 24,561-5), (5)3′,5′-diacetoxyacetophenone (Aldrich 11,738-2), (6) 2-phenylsulfonylacetophenone (Aldrich 34,150-3), (7) 3′-aminoacetophenone (Aldrich13,935-1), (8) 4′-aminoacetophenone (Aldrich A3,800-2), (9)1H-benzotriazole-1-acetonitrile (Aldrich 46,752-9), (10)2-(2H-benzotriazol-2yl)-4,6-di-tert-pentylphenol (Aldrich 42,274-6),(11) 1,1-(1,2-ethane-diyl)bis(3,3,5,5-tetramethylpiperazinone)(commercially available from Goodrich Chemicals), (12)2,2,4-trimethyl-1,2-hydroquinoline (commercially available from MobayChemical), (13) 2-(4-benzoyl-3-hydroxy phenoxy)ethylacrylate, (14)2-dodecyl-N-(1,2,2,6,6-pentamethyl-4-piperidinyl) succinimide(commercially available from Aldrich Chemical Co., Milwaukee, Wis.),(15)2,2,6,6-tetramethyl-4-piperidinyl/β-tetramethyl-3,9-(2,4,8,10-tetraoxospiro(5,5)-undecane) diethyl-1,2,3,4-butane tetracarboxylate(commercially available from Fairmount), (16)N-(p-ethoxycarbonylphenyl)-N′-ethyl-N′-phenylformadine (commerciallyavailable from Givaudan), (17)6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline (commercially availablefrom Monsanto Chemicals), (18)2,4,6-tris-(N-1,4-dimethylpentyl-4-phenylenediamino)-1,3,5-triazine(commercially available from Uniroyal), (19)2-dodecyl-N-(2,2,6,6-tetramethyl-4-piperidinyl)succinimide (commerciallyavailable from Aldrich Chemical Co.), (20)N-(1-acetyl-2,2,6,6-tetramethyl-4-piperidinyl)-2-dodecyl succinimide(commercially available from Aldrich Chemical Co.), (21)(1,2,2,6,6-pentamethyl-4-piperidinyl/β-tetramethyl-3,9-(2,4,8,10-tetraoxo-spiro-(5,5)undecane)diethyl)-1,2,3,4-butane tetracarboxylate(commercially available from Fairmount), (22)(2,2,6,6-tetramethyl-4-piperidinyl)-1,2,3,4-butane tetracarboxylate(commercially available from Fairmount), (23) nickel dibutyl dithiocarbamate (commercially available as UV-Chek AM-105 from Ferro), (24)2-amino-2′,5-dichlorobenzophenone (Aldrich 10,515-5), (25)2′-amino-4′,5′-dimethoxyacetophenone (Aldrich 32,922-3), (26)2-benzyl-2-(dimethylamino)-4′-morpholino butyrophenone (Aldrich40,564-7), (27) 4′-benzyloxy-2′-hydroxy-3′-methylacetophenone (Aldrich29,884-0), (28) 4,4′-bis(diethylamino)benzophenone (Aldrich 16,032-6),(29) 5-chloro-2-hydroxy benzophenone (Aldrich C4,470-2), (30)4′-piperazinoacetophenone (Aldrich 13,646-8), (31)4′-piperidinoacetophenone (Aldrich 11,972-5), (32)2-amino-5-chlorobenzophenone (Aldrich A4,556-4), (33)3,6-bis(2-methyl-2-morpholinopropionyl)-9-octylcarbazole (Aldrich46,073-7), and the like, as well as mixtures thereof.

When present, the optional additives may each, or in combination, bepresent in the ink in any desired or effective amount, such as fromabout 1 percent to about 10 percent by weight of the ink or from about 3percent to about 5 percent by weight of the ink.

The inks disclosed herein may contain any suitable pigment(s) as the atleast one pigment. Examples of suitable pigments include, for example,PALIOGEN Violet 5100 (commercially available from BASF); PALIOGEN Violet5890 (commercially available from BASF); HELIOGEN Green L8730(commercially available from BASF); LITHOL Scarlet D3700 (commerciallyavailable from BASF); SUNFAST Blue 15:4 (commercially available from SunChemical); HOSTAPERM Blue B2G-D (commercially available from Clariant);HOSTAPERM Blue B4G (commercially available from Clariant); Permanent RedP-F7RK; HOSTAPERM Violet BL (commercially available from Clariant);LITHOL Scarlet 4440 (commercially available from BASF); Bon Red C(commercially available from Dominion Color Company); ORACET Pink RF(commercially available from Ciba); PALIOGEN Red 3871 K (commerciallyavailable from BASF); SUNFAST Blue 15:3 (commercially available from SunChemical); PALIOGEN Red 3340 (commercially available from BASF); SUNFASTCarbazole Violet 23 (commercially available from Sun Chemical); LITHOLFast Scarlet L4300 (commercially available from BASF); SUNBRITE Yellow17 (commercially available from Sun Chemical); HELIOGEN Blue L6900,L7020 (commercially available from BASE); SUNBRITE Yellow 74(commercially available from Sun Chemical); SPECTRA PAC C Orange 16(commercially available from Sun Chemical); HELIOGEN Blue K6902, K6910(commercially available from BASF); SUNFAST Magenta 122 (commerciallyavailable from Sun Chemical); HELIOGEN Blue D6840, D7080 (commerciallyavailable from BASE); Sudan Blue OS (commercially available from BASF);NEOPEN Blue FF4012 (commercially available from BASF); PV Fast BlueB2GO1 (commercially available from Clariant); IRGALITE Blue BCA(commercially available from Ciba); PALIOGEN Blue 6470 (commerciallyavailable from BASF); Sudan Orange G (commercially available fromAldrich), Sudan Orange 220 (commercially available from BASF); PALIOGENOrange 3040 (BASE); PALIOGEN Yellow 152, 1560 (commercially availablefrom BASF); LITHOL Fast Yellow 0991 K (commercially available fromBASF); PALIOTOL Yellow 1840 (commercially available from BASF); NOVOPERMYellow FGL (commercially available from Clariant); Ink Jet Yellow 4GVP2532 (commercially available from Clariant); Toner Yellow HG(commercially available from Clariant); Lumogen Yellow D0790(commercially available from BASF); Suco-Yellow L1250 (commerciallyavailable from BASF); Suco-Yellow D1355 (commercially available fromBASF); Suco Fast Yellow D1 355, D1 351 (commercially available fromBASE); HOSTAPERM Pink E 02 (commercially available from Clariant); HansaBrilliant Yellow 5GX03 (commercially available from Clariant); PermanentYellow GRL 02 (commercially available from Clariant); Permanent RubineL6B 05 (commercially available from Clariant); FANAL Pink D4830(commercially available from BASF); CINQUASIA Magenta (commerciallyavailable from DU PONT); PALIOGEN Black L0084 (commercially availablefrom BASE); Pigment Black K801 (commercially available from BASF); andcarbon blacks such as REGAL 330™ (commercially available from Cabot),Nipex 150 (commercially available from Degussa) Carbon Black 5250 andCarbon Black 5750 (commercially available from Columbia Chemical), andthe like, as well as mixtures thereof.

In embodiments, the pigment may comprise from about 0.5 weight percentto about 40 weight percent of the ink, such as from about 1 weightpercent to about 8 weight percent or from about 1.5 weight percent toabout 6 weight percent of the ink. Pigments suitable for use hereininclude particles having an average particle size of from about 15 nm toabout 200 nm, such as from about 15 nm to about 100 nm or from about 15nm to about 50 nm.

There are several challenges in incorporating a pigment into a solidphase change ink composition. Typical ink compositions have manyrelatively non-polar components that can hinder pigment stabilization.At the same time, organic pigments can be anisotropic and have lowerpolarity that can make it difficult to stabilize the pigment particlesin the ink. The low viscosity and high temperatures in use require adispersant that is sufficiently anchored (such as adsorbed, covalentlyor ionically attached, or grafted) to the pigment particle surface suchthat at least a portion of the dispersant is compatible with the lowpolarity vehicle.

In general, pigment particles in a liquid based medium will tend toflocculate unless a suitable stabilization mechanism is employed. Innon-aqueous systems, this can be achieved by adsorbing onto the pigmentparticle surface a molecule that is entirely or partially soluble in theink medium, which prevents, or at least hinders, pigment particles fromapproaching each other too closely such that they interact andflocculate. In order to achieve good thermal stability of the inkdispersion, the dispersant must be strongly associated to the pigmentsurface, such that it does not desorb from the pigment surface uponaging at elevated temperatures. Addition of a suitable synergist assistsin strengthening the pigment/dispersant interaction.

The synergist contains functional groups capable of anchoring, oradsorbing, to the pigment particle surface. The functional groups may bepolar groups. The synergist may be insoluble in a substantial portion ofthe ink vehicle, although it may be soluble in a portion of the inkvehicle.

Examples of suitable functional groups that associate the synergist tothe pigment particles include such functional groups as amines, amides,esters, sulfonates, carboxylic acids, hydroxyl groups, anhydrides,urethanes, ureas and salt groups such as quaternary ammonium salts,combinations thereof and the like. The groups anchor the synergist tothe pigment particles such that the synergist is, for example, adsorbed,attached to or grafted to the pigment particle. The groups can suitablyanchor or adsorb to the pigment particle in any suitable manner, such ashydrogen bonding, covalent or ionic bonding, acid-base reaction, Van derWaals interactions, and the like.

Specific examples of synergists suitable for use herein include, but arenot limited to, for example, SOLSPERSE® 5000 from Lubrizol (a copperphthalocyanine derivatives, for example desirably used with blue, greenor black pigments, SOLSPERSE® 12000 from Lubrizol, for example desirablyused with blue, green or black pigments, SOLSPERSE® 22000 from Lubrizolfor yellow, orange or red pigments, EFKA® 6745 from Ciba-Geigy desirablyused for blue or black pigments and EFKA® 6750 from Ciba-Geigy desirablyused for yellow, orange or red pigments.

In embodiments, the ink composition includes at least one synergist inan amount of from about 0.1% by weight to about 50% by weight of thepigment in the ink composition, for example from about 0.15% by weightto about 10% by weight of the pigment in the ink composition or fromabout 0.5 to about 5% by weight of the pigment in the ink composition.An adequate amount of synergist is sufficient to permit the amount ofdispersant required to stabilize the pigment in the ink to be reducedcompared to the scenario where no synergist is present in the ink, forexample to decreased amounts of about 10 to about 90% by weight of thedispersant without a synergist, such as from about 30 to about 80% byweight of the dispersant without a synergist, or such as from about 60to about 75% by weight of the dispersant without a synergist. The amountof dispersant in the ink composition is not particularly limited, andmay be, for example, from about 0. 1% by weight to about 50% by weightof the pigment in the ink composition. The amount may be low inembodiments, such as from about 0.1% by weight to about 1.5% by weightof the ink composition, with the use of at least one synergist.

As above, the amount of dispersant in the ink composition may be reducedas a result of the use of the synergist. This can be particularlyadvantageous in cases in which the dispersant is tacky, because reducingthe amount of tacky dispersant reduces the tackiness of the overall ink,which can result in less tackiness on an intermediate transfer member orimage receiving surface. The reduced amount of dispersant, however, doesnot adversely affect the stability of the pigment(s) in the inkcomposition due to the use of the synergist.

The effect of reducing the amount of dispersant yet retaining thestability of the ink via addition of a synergist can be expressed interms of particle size measurements with aging. In this regard, particlesize may be measured in any suitable manner, for example using a glasscell and a Malvern ZetaSizer. With storing of the ink in an oven at 120°C. and taking particle size measurements at various times over thecourse of 30 days, the particle size for the ink increases by less than20%, for example less than 15%, from the particle size of the freshlymade ink, when the amount of the dispersant is reduced in the aboveamounts in an ink composition and a synergist is added. In embodiments,the ink as made may have average particle sizes of from about 150 toabout 300 nm.

The synergist is thus a solid that contains functional groups that canstrongly adsorb onto the pigment. The dispersant, on the other hand, issoluble, or at least mainly soluble, in a substantial portion of the inkvehicle. A portion of the dispersant interacts strongly with thesynergist such that the synergist/dispersant combination is stronglyassociated to the surface of the pigment. The combination of thesynergist and the dispersant thus permits the pigment to be effectivelydispersed in the solid ink medium with a desirable reduction in theloading of the dispersant while maintaining particle size stability overtime at elevated temperatures. Pigmented inks are considered stable whenthe particle size growth of the pigment is limited to less than or equalto 15% after being aged at elevated temperature, for example, after 30days at 120° C.

The dispersant thus comprises at least a portion of itself that issoluble in the ink vehicle, which includes at least one functional groupthat has an affinity for the synergist. Overall, the dispersant ispartially or wholly soluble in the medium, but the at least onefunctional group of the dispersant interacts strongly with the synergistwherein the synergist is strongly associated to the surface of thepigment. The soluble portion of the dispersant extends into the inkmedium and provides a barrier, thus preventing or hindering theflocculation of pigment particles.

The dispersant generally comprises a portion, such as polar groups, thatinteract with the synergist and a portion, for example a chain, that iscompatible with the ink vehicle. Polar groups can suitably interact withthe synergist in any suitable manner, such as hydrogen bonding, covalentbonding, acid-base reaction, Van der Waals interactions, and the like.Examples of suitable polar groups include such functional groups asamines, amides, esters, sulfonates, carboxylic acids, hydroxyl groups,anhydrides, urethanes, ureas and salt groups such as quaternary ammoniumsalts, and the like. Examples of the portion of the dispersant that iscompatible with the ink vehicle include groups such as alkyl and alkoxylgroups, which can be linear or branched, saturated or unsaturated andthe like, and may have a chain length of from, for example, about I toabout 50 carbon atoms.

Specific examples of suitable dispersants are polyester dispersants suchas those disclosed in U.S. Pat. No. 6,702,884 and U.S. Pat. No.6,841,590, the disclosures of which are totally incorporated herein byreference. Dispersants may include SOLSPERSE® 16000, SOLSPERSE® 28000,SOLSPERSE® 32500, SOLSPERSE® 38500, SOLSPERSE® 39000, SOLSPERSE® 54000,SOLSPERSE® 17000, SOLSPERSE® 17940, SOLSPERSE® 13240, SOLSPERSE® 19000,as well as mixtures thereof.

Examples of suitable polyester dispersants are disclosed in U.S. Pat.No. 3,996,059, the disclosure of which is totally incorporated herein byreference. The dispersant may be a polyester of the formula

wherein each R₁ is an alkylene group, including linear, branched,saturated, unsaturated, cyclic. substituted, and unsubstituted alkylenegroups containing at least 8 carbon atoms, such as from about 8 to about40 carbon atoms or from about 8 to about 40 or from about 8 to about 20carbon atoms, although the numbers can be outside these ranges; X is (i)an oxygen atom, or (ii) an alkylene group which is attached to thecarbonyl group through an oxygen or nitrogen atom with at least 2 carbonatoms; R₂ is (i) a hydrogen atom, or (ii) a primary, secondary ortertiary amine group or a salt thereof with an acid, or a quaternaryammonium salt group; and n is an integer representing a number ofrepeating groups, for example from 2 to about 20 or from about 2 toabout 10.

Other examples of suitable dispersants include polyalkylene succinimidedispersants such as those disclosed in U.S. Pat. No. 6,858,070, thedisclosure of which is totally incorporated herein by reference.Dispersants can include the Chevron Oronite OLOA 11000, OLOA 11001, OLOA11002, OLOA 11005, OLOA 371, OLOA 375, OLOA 411, OLOA 4500, OLOA 46001,OLOA 8800, OLOA 8900, OLOA 9000, OLOA 9200 and the like, commerciallyavailable from Chevron Oronite Company, as well as mixtures thereof.Other suitable dispersants from Byk-Chemie include examples such as BYKP-105, an unsaturated polycarboxylic acid, BYK 9076, an alkyl ammoniumsalt of high molecular weight co-polymer, BYK 9077, Disperbyk 108, ahydroxy-functional carboxylic acid ester, Disperbyk 116, an acrylateco-polymer, Disperbyk 140, a solution of an alkyl ammonium salt of anacid polymer in 2-methoxy-1-methylethyl acetate, Disperbyk 168, asolution of a high molecular weight block copolymer in a dicarboxylicacid ester, Disperbyk 2000, a solution of a modified acrylate polymer inmethoxypropyl acetate, Disperbyk 2001, a solution of a modified acrylatepolymer in a mixture of methoxypropyl acetate, butylglycol andmethoxypropanol.

Some dispersants are dispersed in volatile solvents (from the supplier),and thus may not be suitable for use directly in certain mixingapparatuses. These dispersants can be pre-treated to remove the volatilesolvent so that the material may optionally be used in the desiredmixing device. The volatile solvents can be removed by heating thedispersant at high temperature, for example at 120° C. (optionally undervacuum) to remove the volatile solvent before being used for the mixingprocess.

In embodiments, a desirable ink composition comprises, in addition todispersant and synergist, from about 40 to about 60% by weight of apolyethylene wax, from about 8 to about 18% by weight of a triamideresin, from about 10 to about 20% by weight of a fatty amide, forexample stearyl steramide, from about 5 to about 15% by weight of arosin ester, from about 0.01 to about 3% by weight of an antioxidant,for example NAUGARD 445, and from about 1 to about 7% by weight of aurethane resin (described in Example 4 of U.S. Pat. No. 6,309,453).

In embodiments, the ink may be prepared by preparing the pigment as aconcentrate in a suitable mixing apparatus, such as for example anextruder, kneader, attritor or the like, for subsequent letdown and highshear mixing, for example, homogenizing, with other components of theink vehicle. In embodiments, in the extrusion process, the synergist,the pigment and the polar resin from the ink formulation, for examplethe triamide resin, are blended together in powder form before beingcharged to the extruder. Although the triamide resin may be considered adispersant for the pigment(s), the blend at this stage can be optionallyfree of dispersants. The resulting extrudate can then be processed withother ink ingredients to form the phase change ink. The contents in theextruder may then be mixed at temperatures of from about 25° C. to about90° C., such as from about 50° C. to about 85° C. or from about 60° C.to about 80° C. at about 5 RPM to about 600 RPM, such as at about 25 RPMto about 100 RPM or at about 40 RPM to about 65 RPM. This mixingprovides the necessary torque to shear the pigment particles, allowingthe polar group of the synergist to anchor onto the pigment surface. Thedispersant may then subsequently be added to the mixture later in theextrusion process, or in embodiments, during the ink making process. Thecontents are extruded to form an extrudate of the pigment, wherein thesheared pigment has been wetted by the resins, synergist and/ordispersant.

Separate from the extrusion process, the other components of the inkvehicle, for example including at least the wax component, are mixed,for example at temperatures of from about 80° C. to about 150° C., suchas from about 80° C. to about 140° C.

The extrudate and the mixed ink vehicle components are then processed bystirring or high shear mixing, for example using a homogenizer or highspeed stirrer or the like, to form a stable pigmented solid phase changeink. The present disclosure is not restricted in terms of the choice ofink components used during preparation of the ink concentrate. Forexample, in some embodiments, both the synergist and the dispersant maybe present during preparation of the ink concentrate.

In further embodiments, the mixing of the extrudate with the remainingcomponents of the ink vehicle may be performed in one or more stages.For example, the homogenization may comprise a first homogenizationprocess with the relatively polar component(s) of the ink and theextrudate, and a second homogenization process wherein the product ofthe first homogenization process is mixed with at least one of therelatively non-polar component of the ink. Relatively polar componentsof the ink may include, but are not limited to, fatty amides (forexample, KEMAMIDE S180), and rosin esters such as a glyceryl abietate(for example, KE-100). Relatively non-polar components of the ink mayinclude, but are not limited to, wax such as polyethylene wax. Bothhomogenization procedures may be conducted at the same or differenttemperatures, for example at temperatures of from about 60° C. to about150° C., or from about 80° C. to about 120° C.

Of course, other processes may also be used to form the ink. Forexample, the dispersant may be present in a mixture to which the pigmentis added, with subsequent addition of the synergist either duringpreparation of the concentrate or the ink itself. This can still resultin an adequate stabilized dispersion of the pigment in the ink vehicle,particularly where the synergist has a stronger affinity for the pigmentsurface than the dispersant. Furthermore, alternative means ofprocessing may be used for both the preparation of the ink concentrateand the ink itself. For example, the ink concentrates or the inks can beagitated or mixed by any suitable means, including a mechanical ormagnetic stirrer, a high speed mixer, an attritor, a homogenizer, asonificator, a microfluidizer, and the like, with or without an optionalgrinding medium, such as stainless steel balls, ceramic chips, and thelike.

The ink formed may be filtered by any suitable process, for example byfiltering with a screen at temperatures of from about 90° C. to about150° C. Filtration of the prepared ink can be performed using variousdepth filters, such as for example nylon, polysulfone, and glass fiberfilters having absolute ratings of, for example, 6 microns or 1 micron.

The inks disclosed herein may exhibit Newtonian behavior from about 100°C. to 130° C., such as from about 110° C. to about 120° C., at a shearrate of about 10⁻² to about 10⁴ s⁻¹, such as from about 10⁻¹ to about10³ s⁻¹.

Phase change ink jet processes are well known and are described, forexample, in U.S. Pat. Nos. 4,601,777, 4,251,824, 4,410,899, 4,412,224and 4,532,530, the disclosures of which are incorporated herein byreference in their entirety.

Ink jetting devices are known in the art. As described in U.S. Pat. No.6,547,380, the disclosure of which is totally incorporated herein byreference, ink jet printing systems are generally of two types:continuous stream and drop-on-demand. In continuous stream ink jetsystems, ink is emitted in a continuous stream under pressure through atleast one orifice or nozzle. The stream is perturbed, causing it tobreak up into droplets at a fixed distance from the orifice. At thebreak-up point, the droplets are charged in accordance with digital datasignals and passed through an electrostatic field that adjusts thetrajectory of each droplet in order to direct it to a gutter forrecirculation or a specific location on a recording medium. Indrop-on-demand systems, a droplet is expelled from an orifice directlyto a position on a recording medium in accordance with digital datasignals. A droplet is not formed or expelled unless it is to be placedon the recording medium. Different types of drop-on-demand ink jetsystems for non-aqueous inks exist. One type of drop-on-demand system isa piezoelectric device that has as its major components an ink filledchannel or passageway having a nozzle on one end and a piezoelectrictransducer near the other end to produce pressure pulses. Another typeof drop-on-demand system is known as acoustic ink printing. As is known,an acoustic beam exerts a radiation pressure against objects upon whichit impinges. Thus, when an acoustic beam impinges on a free surface(i.e., liquid/air interface) of a pool of liquid from beneath, theradiation pressure which it exerts against the surface of the pool mayreach a sufficiently high level to release individual droplets of liquidfrom tile pool, despite the restraining force of surface tension.Focusing the beam on or near the surface of the pool intensifies theradiation pressure it exerts for a given amount of input power.

Printed images may be generated with the ink described herein byincorporating the ink into an ink jet device, for example an acousticink jet device or a piezoelectric ink jet device, heating the ink to asuitable jetting temperature, and concurrently causing droplets of themolten ink to be ejected in a pattern onto a substrate such as anintermediate transfer medium or directly onto paper or transparencymaterial, which can be recognized as an image. The ink is typicallyincluded in the at least one reservoir connected by any suitable feedingdevice to the ejecting channels and orifices of the ink jet head forejecting the ink. In the jetting procedure, the inkjet head may beheated, by any suitable method, to the jetting temperature of the inks.The phase change inks are thus transformed from the solid state to amolten state for jetting. In a typical design of a piezoelectric ink jetdevice, the image is applied by jetting appropriately colored inksduring four to eighteen rotations (incremental movements) of a substratesuch as an image receiving member or intermediate transfer member withrespect to the ink jetting head, that is, there is a small translationof the printhead with respect to the substrate in between each rotation.This approach simplifies the printhead design, and the small movementsensure good droplet registration.

The inks can also be employed in indirect (offset) printing inkjetapplications, wherein when droplets of the melted ink are ejected in animagewise pattern onto a recording substrate, the recording substrate isan intermediate transfer member and the ink in the imagewise pattern issubsequently transferred from the intermediate transfer member to afinal recording substrate, such as paper or transparency.

Embodiments described above will now be further illustrated by way ofthe following examples.

EXAMPLE 1

Inks were prepared using an attritor for preparation of the inkconcentrate, as summarized below. Ink concentrate 1 was prepared asfollows: a Szegvari 01 Attritor equipped with ⅛ inch stainless steelballs was heated to 120° C. and charged with a pre-melted mixturecontaining triamide resin 6 (113.4 g), SOLSPERSE® 13240 (21.0 g), andNAUGARD 445 (0.25 g). To the stirred mixture was added slowly HOSTAPERMBlue B4G (21.0 g), and then SOLSPERSE® 5000 (0.42 g) as the synergist.The mixture was stirred for 16 hours at a speed of 250 RPM and atemperature of 120° C. A diluent solution of KE100 (36.0 g), KEMAMIDES-180 (40.5 g), urethane resin (12.0 g), NAUGARD 445 (0.25 g), andpolyethylene wax (156.0 g) was pre-melted at 120° C. The molten diluentsolution was then poured slowly into the stirred ink concentrate (55.7g), and stirred at 120° C. for a further 1 hour.

The ink was filtered and then immediately placed in a glass cell, usedfor particle size measurements on a Malvern ZetaSizer. The cell wasstored in an oven at 120° C.; particle size measurements were taken atvarious times over the course of 30 days. The particle size for thefreshly filtered ink was 234 nm, and after 30 days aging at 120° C., theparticle size was 229 nm.

EXAMPLE 2

Ink 2 was prepared using the same method as for Example 1, but thesynergist was not added. The particle size for the freshly filtered inkwas 283 nm, and after 30 days aging at 120° C., the particle size was372 nm.

EXAMPLE 3

Ink 3 was prepared using the same method as for Example 1, but a reducedamount of SOLSPERSE® 13240 (13.7 g) was used. The particle size for thefreshly filtered ink was 255 nm, and after 30 days aging at 120° C., theparticle size was 282 nm.

The effect of the synergist can be seen both in terms of nominalparticle size, and particle size stability. The inks without synergistexhibited larger particle size and size growth than did the inkscontaining synergist. Furthermore, addition of the synergist enabled theuse of less dispersant, while maintaining thermal stability in terms ofparticle size and particle size growth.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also,various presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art, and are also intended to beencompassed by the following claims.

1. A phase change ink composition comprising an ink vehicle and at leastone pigment, wherein the ink composition is substantially solid at roomtemperature and includes (1) at least one dispersant soluble in the inkvehicle and (2) at least one solid synergist insoluble in the inkvehicle, and wherein the average particle size of the ink composition,when stored at 120° C. for 30 days, increases by less than 20% from anaverage particle size of the ink composition when freshly made.
 2. Thephase change ink composition according to claim 1, wherein the averageparticle size of the ink composition, when stored at 120° C. for 30days, increases by less than 15% from an average particle size of theink composition when freshly made.
 3. The phase change ink compositionaccording to claim 1, wherein the average particle size of the freshlymade ink composition is from about 150 nm to about 300 nm.
 4. The phasechange ink composition according to claim 1, wherein the at least onesolid synergist includes a functional group that adsorbs to the surfaceof the at least one pigment.
 5. The phase change ink compositionaccording to claim 4, wherein the functional group includes amines,amides, esters, sulfonates, carboxylic acids, hydroxyl groups,anhydrides, urethanes, ureas, quaternary ammonium salts and combinationsthereof.
 6. The phase change ink composition according to claim 4,wherein the at least one dispersant comprises a portion interactive withthe at least one solid synergist and a portion soluble in the inkvehicle.
 7. The phase change ink composition according to claim 6,wherein the ink vehicle includes at least one wax, and wherein a portionof the at least one dispersant is soluble in the at least one wax. 8.The phase change ink composition according to claim 7, wherein the atleast one solid synergist is insoluble in the at least one wax.
 9. Thephase change ink composition according to claim 1, wherein the inkvehicle comprises at least one wax and at least one amide resin.
 10. Thephase change ink composition according to claim 9, wherein the at leastone amide resin has a formula of:

wherein R₁ is (i) an alkylene group having from about 3 carbon atoms toabout 200 carbon atoms, (ii) an arylene group having from about 6 carbonatoms to about 200 carbon atoms, (iii) an arylalkylene group having fromabout 7 carbon atoms to about 200 carbon atoms, or (iv) an alkylarylenegroup having from about 7 carbon atoms to about 200 carbon atoms, R_(a),R_(b) and R_(c) are each independently (i) a hydrogen atom, (ii) analkyl group having from about 1 carbon atoms to about 200 carbon atoms,(iii) an aryl group having from about 6 carbon atoms to about 200 carbonatoms, (iv) an arylalkyl group having from about 6 carbon atoms to about200 carbon atoms, or (v) an alkylaryl group having from about 6 carbonatoms to about 200 carbon atoms, and R_(d), R_(e) and R_(f) are eachindependently (i) an alkyl group having from about 1 carbon atoms toabout 200 carbon atoms, (ii) an aryl group having from about 6 carbonatoms to about 200 carbon atoms, (iii) an arylalkyl group having fromabout 6 carbon atoms to about 200 carbon atoms, or (iv) an alkylarylgroup having from about 6 carbon atoms to about 200 carbon atoms. 11.The phase change ink composition according to claim 9, wherein the atleast one wax is a polyethylene wax.
 12. The phase change inkcomposition according to claim 6, wherein the portion of the dispersantinteractive with the at least one solid synergist is at least onefunctional group of amines, amides, esters, sulfonates, carboxylicacids, hydroxyl groups, anhydrides, urethanes, ureas, salt groups orcombinations thereof.
 13. The phase change ink composition according toclaim 6, wherein the portion of the dispersant soluble in the inkvehicle comprises linear or branched alkyl or alkoxyl groups having fromabout 1 to about 50 carbon atoms.
 14. A phase change ink compositioncomprising an ink vehicle and at least one pigment, wherein the inkcomposition includes at least one dispersant for the at least onepigment in an amount of from about 0.1% by weight to about 1.5% byweight of the ink composition, the at least one dispersant being solublein the ink vehicle, and at least one solid synergist that is insolublein the ink vehicle and is present in an amount of from about 0.1% byweight to about 5% by weight of the pigment in the ink composition. 15.The phase change ink composition according to claim 14, wherein the inkvehicle includes a wax, the at least one solid synergist being insolublein the wax and including a functional group that adsorbs to the surfaceof the at least one pigment.
 16. The phase change ink compositionaccording to claim 15, wherein the functional group includes amines,amides, esters, sulfonates, carboxylic acids, hydroxyl groups,anhydrides, urethanes, ureas, quaternary ammonium salts or combinationsthereof.
 17. The phase change ink composition according to claim 15,wherein the at least one dispersant comprises a portion interactive withthe at least one solid synergist and a portion soluble in the wax. 18.The phase change ink composition according to claim 17, wherein theportion of the dispersant interactive with the at least one solidsynergist is at least one functional group of amines, amides, esters,sulfonates, carboxylic acids, hydroxyl groups, anhydrides, urethanes,ureas, salt groups or combinations thereof, and wherein the portion ofthe dispersant soluble in the ink vehicle comprises linear or branchedalkyl or alkoxyl groups having from about 1 to about 50 carbon atoms.19. The phase change ink composition according to claim 15, wherein theink vehicle further comprises at least one amide resin and at least oneurethane resin.
 20. A phase change ink composition comprising an inkvehicle and at least one pigment, the ink vehicle comprising at leastone wax and at least one amide resin, wherein the ink compositionincludes at least one dispersant for the at least one pigment and atleast one solid synergist, the at least one solid synergist including afunctional group that adsorbs to the surface of the at least one pigmentand being insoluble in the wax, the at least one dispersant comprising aportion interactive with the at least one solid synergist and a portionsoluble in the wax.